走出歌德的阴影: 迈向更加科学的植物系统学

传统的植物学理论中, 被子植物雌蕊的基本单位心皮被认为是变态的叶(即大孢子叶)通过纵向对折和内卷演化而来。该理论造成了被子植物和裸子植物之间不可逾越的鸿沟。近年来提出的一统理论认为被子植物的心皮由长胚珠的枝和包裹这个枝的叶共同组成, 从而弥合了被子植物与裸子植物之间的鸿沟。最近, 当代植物学界两大权威人物Peter R. Crane和Peter K. Endress分别撰文, 发表了不同于传统理论的观点。Endress认为, 心皮由胚珠和叶性器官组成; 而Crane认为, 所有的胚珠都长在枝上。结合二者的结论, 不难得出“心皮实际上等同于一个长胚珠的枝加上一个叶”的论断。这在某种意义上等于认同了一统理论的观点。两位权威人物观点的转变预示着植物学理论将很快发生根本性的转变。该文向国内植物学同行通报这一最新动态, 以期让我国学者能够了解最新理论。     

Botany without borders: barcoding in focus

This recent meeting, held on the campus of the University of British Columbia, attracted 1200 delegates and a vast array of talks, but was notable for a remarkable showing of talks and posters on DNA barcoding in plants, spread through many sessions. The Canadian Centre for DNA Barcoding defines barcoding as ‘species identification and discovery through the analysis of short, standardized gene regions known as DNA barcodes’. This approach is somewhat controversial in animals ( Rubinoff et al., 2006 ), although it has been shown to be useful and reliable in many metazoan taxa ( Meyer & Paulay 2005 ; Hajibabaei et al., 2007 ), in which the mitochondrial cytochrome oxidase I (COI) gene is used. However, in land plants, COI evolves far too slowly to be useful, and there is no obvious single universal alternative ( Fazekas et al., 2008 ). Genes that work well in one taxon may perform poorly in other taxa. Additionally, some perfectly good plant species, reproductively isolated and morphologically and ecologically distinct, are too young to show much sequence divergence at most loci. Nevertheless, as we saw at this conference, progress has been made towards identifying genes that serve many of the functions of DNA barcodes, at least in some plant taxa.     

Contributions of plant molecular systematics to studies of molecular evolution

Dobzhansky stated that nothing in biology makes sense except in the light of evolution. A close corollary, and the central theme of this paper, is that everything makes a lot more sense in the light of phylogeny. Systematics is in the midst of a renaissance, heralded by the widespread application of new analytical approaches and the introduction of molecular techniques. Molecular phylogenetic analyses are now commonplace, and they have provided unparalleled insights into relationships at all levels of plant phylogeny. At deep levels, molecular studies have revealed that charophyte green algae are the closest relatives of the land plants and suggested that liverworts are sister to all other extant land plants. Other studies have suggested that lycopods are sister to all other vascular plants and clarified relationships among the ferns. The impact of molecular phylogenetics on the angiosperms has been particularly dramatic – some of the largest phylogenetic analyses yet conducted have involved the angiosperms. Inferences from three genes (rbcL, atpB, 18S rDNA) agree in the major features of angiosperm phylogeny and have resulted in a reclassification of the angiosperms. This ordinal-level reclassification is perhaps the most dramatic and important change in higher-level angiosperm taxonomy in the past 200 years. At lower taxonomic levels, phylogenetic analyses have revealed the closest relatives of many crops and model organisms for studies of molecular genetics, concomitantly pointing to possible relatives for use in comparative studies and plant breeding. Furthermore, phylogenetic information has contributed to new perspectives on the evolution of polyploid genomes. The phylogenetic trees now available at all levels of the taxonomic hierarchy for angiosperms and other green plants should play a pivotal role in comparative studies in diverse fields from ecology to molecular evolution and comparative genetics.     

Angiosperm leaves associated with Sinocarpus infructescences from the Yixian Formation (mid-Early Cretaceous) of NE China

Typical angiosperm dicot leaves are discovered closely associated with reproductive organs of Sinocarpus decussatus from the Yixian Formation, NE China. Leaves are of first rank, small, with fine texture, and with distinct petiole and lamina. Venation pattern is craspedodromous, of at least three discrete orders of veins irregularly arranged. Leaf margin is serrate, with glandular teeth of chloranthoid type. The new Sinocarpus material is better preserved and more complete than the type specimen. It yields support for previous interpretations of reproductive characters and shows that the inflorescences were compound, perhaps combining alternate and opposite phyllotaxis, and that seeds were arranged in two rows, each row with about ten seeds. While these new reproductive characters do not provide further resolution to the systematic assignment of Sinocarpus, the associated leaves, believed to be from the same plant, support previous interpretation of Sinocarpus as a basal eudicot, and particularly close to Ranunculales.     

Sinocarpus decussatus gen. et sp. nov., a new angiosperm with basally syncarpous fruits from the Yixian Formation of Northeast China

An Early Cretaceous angiosperm, Sinocarpus decussatus gen. et sp. nov., is described from the Yixian Formation in Liaoning, China, based on an infructescence fragment. It is probably ebracteate, consisting of one terminal fruit and two pairs of pedicellate lateral fruits arranged decussately. Carpels are probably borne on a small convex receptacle. There are no distinct remnants of a perianth although fragments observed at the base of immature fruits may represent perianth parts. No remnants of androecial parts have been observed, and it is unknown whether the flowers were unisexual or bisexual. The basally syncarpous ovary is superior and composed of 3 or 4 carpels. Each carpel contains about 10 anatropous ovules/seeds borne along the linear placentae. Seeds are flattened and embedded in a thick amorphous material. The character combination of Sinocarpus indicates a systematic position among the basal grade of eudicots or the basal core eudicots, and particularly shows similarities to extant Ranunculaceae, Buxaceae, and Myrothamnaceae, but based on the available data the fossil cannot unambiguously be placed in any modern family.     

中国植物系统和进化生物学研究进展

植物系统和进化生物学旨在探讨植物物种多样性的起源、多样化及其进化的机制, 是综合性越来越强的研究领域。2017年在深圳召开的第19届国际植物学大会(IBC 2017)为中国学者提供了一次难得的展示自身实力的机会和舞台, 同时也极大地推动了中国植物系统与进化生物学领域的研究。值此大会召开5周年之际, 本文拟就中国系统和进化生物学领域近年来取得的主要进展和突破做一简要回顾, 以帮助读者了解中国植物系统和进化研究的发展态势, 并在此基础上展望未来该领域的发展趋势以及面临的机遇和挑战。在过去5年中, 中国学者在植物系统与进化生物学领域的各个方面均取得了令人鼓舞的成绩和突破, 涉及植物起源和物种多样性格局的演变、植物分类和系统发生重建、物种形成和适应性进化、种间互作和协同进化、新性状的起源及其进化发育机制、植物多倍化的机制和多倍体进化、物种濒危机制和物种保护以及栽培植物的起源和驯化等等。这些研究成果不仅在数量上而且在质量上有显著提升, 受到国际学界的广泛关注, 意味着中国学者已经成为国际该领域研究的重要力量, 并将在国际植物系统和进化研究领域发挥更大的作用。     

Basal titanosauriform (Dinosauria, Sauropoda) teeth from the Lower Cretaceous Yixian Formation of Liaoning Province, China

The Yixian Formation of Liaoning Province, People's Republic of China has yielded a diverse fauna of non-avian dinosaurs, but is dominated by small-bodied taxa. Here, we describe a series of isolated teeth from the Lujiatun Beds of the formation that are referable to a basal titanosauriform sauropod. Some of the teeth possess a distinctive circular boss on the lingual surface, which suggests that they are referable to cf. Euhelopus sp. This identification provides some additional support for biostratigraphical correlations between the Jehol Group and the Mengyin Formation of Shandong Province that suggest an Early Cretaceous age for the latter unit. Moreover, the titanosauriform affinities of the teeth provide further evidence for the dominance of this sauropod clade in eastern Asia during the Cretaceous.     

Adaptive evolution in the photosensory domain of phytochrome A in early angiosperms

Flowering plant diversity now far exceeds the combined diversity of all other plant groups. Recently identified extant remnants of the earliest-diverging lines suggest that the first angiosperms may have lived in shady, disturbed, and moist understory habitats, and that the aquatic habit also arose early. This would have required the capacity to begin life in dimly lit environments. If so, evolution in light-sensing mechanisms may have been crucial to their success. The photoreceptor phytochrome A is unique among angiosperm phytochromes in its capacity to serve a transient role under conditions where an extremely high sensitivity is required. We present evidence of altered functional constraints between phytochrome A (PHYA) and its paralog, PHYC. Tests for selection suggest that an elevation in nonsynonymous rates resulted from an episode of selection along the branch leading to all angiosperm PHYA sequences. Most nucleotide sites (95%) are selectively constrained, and the ratio of nonsynonymous to synonymous substitutions on branches within the PHYA clade does not differ from the ratio on the branches in the PHYC clade. Thus, positive selection at a handful of sites, rather than relaxation of selective constraints, apparently has played a major role in the evolution of the photosensory domain of phytochrome A. The episode of selection occurred very early in the history of flowering plants, suggesting that innovation in phyA may have given the first angiosperms some adaptive advantage.     

Repeated evolution of a reproductive polyphenism in plants is strongly associated with bilateral flower symmetry

1. Download : Download high-res image (93KB)
2. Download : Download full-size image

     

中国逍遥蛛科化石新属种（蜘蛛目，逍遥蛛科）

记述产自中国辽西的逍遥蛛科化石1新属：白垩逍遥蛛属Cretadromus gen．nov．,1新种：辽宁白垩逍遥蛛Cretadromus liaoningensis sp．nov．：这是逍遥蛛科化石在中国的首次发现,也是逍遥蛛科在晚侏罗世-早白垩世的首次报道。标本采白辽宁省凌源市大王杖子晚侏罗世-早白垩世义县组地层,现存于大连自然博物馆：     

Comments on the present situation of DNA systematics in higher plants

Short comments were made to the present situation of DNA systematics in higher plants, particularily on intraspecific variations in chloroplast DNA. Comments were also extended to DNA plant geography.     

分子系统学原理及其在林木上的应用

综述了林木分子系统学的是新研究进展,分析了现代分子生物学方法的不断改进给林木系统学研究带来的革命性进展,阐述了RAPD,cpDNA,rDNA等在林木分子系统学研究中的应用及取得的成果,评述了各种不同分子标记的适用范围以及对相关基因进化规律的认识,同时提出了这些分子标记在分子系统学研究中应注意的一些问题。     

Pollen Morphology and Taxonomic Position of the Genus Pentaphragma Wall. (Pentaphragmataceae)

The pollen morphology of some Pentaphragma Wall, species has been studied by light- and electron microscopy. To improve the rehydration of the dried material used, compound fixatives have been applied. Intine-held vesicles and fibrillar network in gaps and spaces of the exine stain positively for protein. The pollen morphology of the genus differs strongly from that of Campanulaceae, and shows distinctive characters of its own. Hence from a palynological point of view it appears correct to place the genus in a separate family.     

Natural taxonomic categories of angiosperms obey Benford's law,but artificial ones do not

Benford's phenomenological law gives the expected frequencies of the first significant digit (i.e., the leftmost non-zero digit) of any given series of numbers. According to this law, the frequency of 1 is higher than that of 2; this in turn appears more often than 3, and so on decreasing until 9. Similarly, Benford's law can also be applied to the first two significant digits (i.e., from 10 to 99), and so on. We applied Benford's law to sets of taxonomic data sets consisting of the number of taxa included in taxa of higher rank. We chose the angiosperms (Magnoliophyta) as a model case, because they are very diverse, are monophyletic, and a consensus on taxonomy of orders and families has been achieved (classification APG III), and we used as sets of data the number of species, genera, families, and orders. Only the number of species per family and per order are Benford's sets, but the remaining data sets do not obey Benford. Furthermore, in the case of the analysis of the first two significant digits of species per genus, the deviation from Benford was very large, but they fit to a power law. Given that the conformity to Benford's law is fulfilled for ‘natural' taxonomic categories of angiosperms (i.e., species and family), but not for those with more artificiality (genus), we speculate, ‘the more natural, the more Benford'.     

Gynoecium diversity and systematics of the Magnoliales and winteroids

Carpel and ovule structure was compared in representatives of all 11 families of the Magnoliales (Annonaceae, Canellaceae, Degeneriaceae, Eupomatiaccae, Himantandraceae, Magnoliaceae, Myristicaceae) and winteroids (Austrobaileyaceae, Illiciaceae, Sehisandraceae, Winteraceae). Special attention was paid to features that are constant at family level. Bisexual flowers are always protogynous. In all representatives studied the carpels are closed at anthesis. Caipel closure is attained in three different ways: (1) postgenital fusion of inner surfaces (Degeneriaceae, Eupomatiaccae. Winteraceae), or (2) occlusion by secretion (Austrobaileyaceae, Sehisandraceae), or (3) a combination of (1) and (2): in Annonaceae, Canellaceae, Myristicaceae there is a conspicuous secretory canal in the innermost part of the ventral slit; in Illiciaceae and Magnoliaceae there is a narrow canal in the innermost part of the ventral slit; and in Himantandraceae the ventral slit is postgenilally fused in the style but completely open in the ovary. In most families the carpels have a double stigmalic crest or they have two tips in the transversal symmetry plane (i.e. at right angles to the median plane). Stigmas are unicellular papillate in most families but the papillae are bi-to multicellular (uniseriate) in Degeneriaceae and Eupomatiaceae. An unusual cryptic exlracarpellary compitum was found in Himantandraceae and Sehisandraceae. Intrusive oil cells were found in the carpel epidermis of Illiciaceae and Sehisandraceae. Mature ovules vary in length between 0.15 and 1.1 mm. The outer integument is fully annular (not semiannular) in Degeneriaceae, Himantandraceae, Canellaceae, Myristicaceae, and Illiciaceae. A rudimentary aril occurs in Canellaceae, and originates at the same site as in arillate Annonaceae and Myristicaceae. The results most strongly support an Annonaceae-Myristicaceae-Canellaceae alliance, to some degree also an Eupomatiaccac-Degeneriaceae-Himantandraceae-Magnoliaceae alliance, and an Illiciaceae-Schisandraceae-Winteraccae-Austrobaileyaceae alliance.